The present disclosure relates to a fixing device for fixing toner, an image forming apparatus including the fixing device, and a method for controlling the fixing device.
An image forming apparatus such as a copier, a multifunction peripheral, a printer, or a facsimile apparatus is equipped with a plurality of motors for driving rotating members to rotate, which includes various rollers and a photoreceptor drum. Further, conventionally, it is common to perform rotation control (operational control) of the motors by software control using a control device (processor) such as a CPU or a microcomputer. However, if runaway of a control device occurs, excessive force may be applied to a motor, a transmission portion for transmitting motor power, or a portion driven by the motor power, resulting in a breakdown. Therefore, there is known a technique to prevent runaway of a carriage (head moving portion of an ink jet printer apparatus) due to runaway of the CPU.
Specifically, there is known a carriage drive control device for a carriage drive motor for driving the carriage to move in a printer, which includes a pulse signal output unit that outputs a pulse signal whose number of pulses is proportional to a movement amount of the carriage, a control unit that output a control signal for controlling the carriage drive motor by feedback control using the pulse signal received from the pulse signal output unit so as to make a predetermined speed pattern including acceleration, constant speed, and deceleration, a carriage driving circuit that drives the carriage drive motor on the basis of the control signal received from the control unit, and a pulse period detection circuit constituted of a hardware logic circuit that detects a pulse period of the pulse signal received from the pulse signal output unit and compares the detected pulse period with a lower limit value having a predetermined set pulse period, so as to output a stop instruction signal for instructing the carriage driving circuit to forcedly stop the carriage drive motor when the detected pulse period becomes smaller than the lower limit value.
First, an electrophotography type image forming apparatus is equipped with a fixing device for fixing a toner image transferred onto a paper sheet. For instance, the fixing device includes a heating rotating member (for example, a roller) which is heated by a heat generating member so as to heat toner, and a pressing rotating member (for example, a roller) which is pressed to the heating rotating member. A paper sheet onto which a toner image is transferred is permitted to pass through a nip between the heating rotating member and the pressing rotating member, and hence the fixing process is performed.
Further, in the case where the heating rotating member and the pressing rotating member always contact with each other, there are demerits such as that it is difficult to remove a jammed paper sheet in the nip and that lifetime of the rotating member is shortened. Therefore, the fixing device may include a mechanism for decreasing fixing pressure by separating the heating rotating member from the pressing rotating member during interval between printing processes, while permitting the heating rotating member and the pressing rotating member to be close to each other for making a pressed state (contact state) with pressure (fixing pressure) of the nip in the printing process.
In this mechanism, a motor may be used as a drive source for moving the rotating member. Further, conventionally, a sensor for detecting a position of the rotating member or a rotation angle of the motor is disposed so that a control device such as a CPU for controlling rotation of the motor receives an output of the sensor, the control device recognizes a position of the rotating member or a state of the motor, and hence a rotation direction, a rotation angle, and stop of the motor are controlled by software control.
However, if the control device such as the CPU runs away, the motor drive is continued (locked state is continued) even if the rotating member becomes a limit position. Therefore, the motor or a component such as a gear included in the mechanism for moving the rotating member may be broken down. In addition, when adopting a structure in which the control device performs software control of the motor, a CPU port for receiving the output of the sensor may be lacking, or wiring may be complicated. In addition, it is necessary to install software for the control. In this way, there is a demerit due to the structure in which the control device such as the CPU receives the output of the sensor so as to perform software control.
Here, the above-mentioned known carriage drive control device is a device related to movement of the carriage and is not related to adjustment of the fixing pressure of the fixing device. In addition, the device cannot be used without a thing for generating a pulse in accordance with motor rotation (for example, an encoder). In addition, a high accuracy encoder is expensive, and hence there is a demerit that manufacturing cost increases.